With growing environmental awareness in recent years, technology needs for an energy management has increased. EMS such as an HEMS (home energy management system) that conducts the energy management at home, a BEMS (building energy management system) that conducts the energy management in collective housings or buildings, or a CEMS (city energy management system) that conducts the energy management in an area of community are expected from a customer side that consumes energy. A smart meter or an AMI (advanced metering infrastructure) that automatically reads a power meter, and a smart grid that stabilizes an electric power distribution/electric power transmission system have been demanded from a power company side that generates energy, and demonstration experiments have been promoted. Further, a smart city concept of performing those techniques in urban areas together has been also studied.
In order to realize those energy-related management systems, it is essential to secure an infrastructure of communication means. There are various candidates such as a radio communication, a wired communication, an optical communication, and a power carrier communication as the communication means. It seems that suitable means is selected depending on an environment constructed as the infrastructure. Among those communications, the radio communication is excellent in terms of installation, ease of maintenance, the low cost of a device class, and scalability, and highly expected.
When the radio communication is used as the communication infrastructure means, the consideration of an installation environment is also required, and the optimization is required depending on an intended purpose. For example, in the smart meter, there is required that a large number of radio terminals conduct a communication with each other periodically (every 30 minutes) in a relatively short distance area within about several 100 m to 1 km. On the other hand, an emergency response is required in the smart grid, there is a need to conduct a long-distance communication of about 10 km at a high speed (a low delay or a short period). As an example of the emergency response, there are short-circuiting caused by a damage to electric wires, and an emergency stop of a power distribution.
When meter reading data collection of the smart meter, and device data collection of the smart grid are “steady”, the emergency response in the smart grid can be regarded as “unsteady”.
A communication transmission distance required for the radio communication is different in the communication between the steady situation and the unsteady situation described above. An increase in the transmission distance in the unsteady situation can be performed by increasing a transmission radio wave power of the radio communication device. However, a transmission power that enables a communication at a distance of several km is large, and a power consumption of the radio communication device also increases. Therefore, in the steady situation, it is preferable to conduct a short-distance radio communication with a small transmission power from the viewpoint of the power consumption.
As means for changing the transmission power of the radio communication, for example, PTL 1 discloses means for changing a power of a radio relay station. According to this PTL 1, when plural base stations of cellular phones are provided, and a communication traffic volume of a certain base station is high, signals of terminals present in an area of that base station are transmitted to another base station by increasing a relay station power.
Also, PTL 2 discloses means for increasing the power in the radio base station. According to this PTL 2, in a communication between the base station and the terminal, when the base station conducts an emergency call, and the radio communication does not normally operate (not connected, or not successful in communication), the base station increases the power to facilitate a connection between the base station and the terminal.